This project is a three year longitudinal "double blind" clinical trial to study the effect of mouthrinsing with a daily0.05 percent neutral sodium fluoride rinse upon the development of root and coronal caries in adults. The study population will consist of approximately 1200 people, 18-65 years of age, who reside in a community where the drinking water contains less than 0.3 ppm fluoride and where the population is relatively less stable (less tha 15% annual attrition rate). The individual subjects must have a high caries susceptibility and at least 50% of the natural teeth, excluding third molars.